The present invention relates to a cryogenic refrigeration system, and more particularly to a countermeasure against an impurity in the system.
A cryogenic refrigeration system employing a combination of a JT refrigerator and a pre-cooling refrigerator is known in the prior art, as disclosed in, for example, Japanese Laid-Open Patent Publication No. 9-229503. A GM refrigerator, or the like, is used as the pre-cooling refrigerator.
The JT refrigerator is a refrigerator that generates coldness of a cryogenic level by subjecting a high pressure helium gas from a compressor to a Joule-Thomson expansion through a JT valve. On the other hand, the GM refrigerator is a refrigerator that generates a coldness by expanding a high pressure helium gas from a compressor through the reciprocating movement of a displacer. The GM refrigerator as a pre-cooling refrigerator pre-cools the helium gas in the JT refrigerator before the Joule-Thomson expansion by using the coldness.
Some cryogenic refrigeration systems including a JT refrigerator and a pre-cooling refrigerator are provided with a heat-collecting heat exchanger that exchanges heat between a high pressure helium and a low pressure helium in the systems. Such a cryogenic refrigeration system performs a heat collecting operation within the system, thereby improving the operating efficiency.
However, if water as an impurity exists in the helium as a refrigerant, the water is frozen in the heat-collecting heat exchanger or in a pipe there around, which may clog the passageway. In view of this, a system as follows has been proposed in the art (see Japanese Laid-Open Patent Publication No. 2001-108320), in which a circuit for eliminating the clog in the passageway is added.
FIG. 9 illustrates such a cryogenic refrigeration system (100), including a compressor unit (101) and a refrigerator unit (102). The compressor unit (101) includes a low pressure side compressor (103) and a high pressure side compressor (104). The refrigerator unit (102) includes a GM refrigerator (112) having a first heat station (113) and a second heat station (114), and a JT refrigerator (111) having a JT valve (116).
In the compressor unit (101), a discharge side pipe (105) is connected to the discharge side of the high pressure side compressor (104), and a suction side pipe (109) is connected to the suction side of the low pressure side compressor (103). Oil separators (106) and an adsorber (107) are provided along the discharge side pipe (105). The discharge side pipe (105) diverges into two high pressure pipes (108, 110). The first high pressure pipe (108) is connected to the JT refrigerator (111), and the second high pressure pipe (110) is connected to the GM refrigerator (112). A flow rate control valve (135), and a switching valve (134) for preventing a refrigerant at room temperature from flowing into the refrigerator unit (102) when the operation of the system is shut down, are provided along the first high pressure pipe (108). Note that a check valve (126) for preventing a refrigerant at room temperature from flowing into the refrigerator unit (102) when the operation of the system is shut down is provided also along the suction side pipe (109).
A JT circuit (115) in the refrigerator unit (102) includes a high pressure line (117) and a low pressure line (118), and the JT valve (116) is provided along the high pressure line (117). A first pre-cooling section (119) in the first heat station (113) and a second pre-cooling section (120) in the second heat station (114) are provided along the high pressure line (117). Moreover, first to third heat-collecting heat exchangers (121-123) for exchanging heat between the high pressure helium gas flowing along the high pressure line (117) and the low pressure helium gas flowing along the low pressure line (118) are provided in the JT circuit (115).
As clog elimination means for eliminating a clog when the passageway of the first heat exchanger (121) is clogged, the cryogenic refrigeration system (100) includes a supply pipe (124) for supplying the discharge gas from the compressors (103, 104) to the outlet side of the high pressure side passageway of the first heat exchanger (121), and a collection pipe (125) for collecting the discharge gas, which has flowed through the high pressure side passageway of the first heat exchanger (121), into the suction side pipe (109) of the compressors (103, 104). In order to prevent the refrigerant from flowing into the supply pipe (124) and the collection pipe (125) during a normal cooling operation, a switching valve (127) is provided along the supply pipe (124) and a switching valve (129) is provided along the collection pipe (125). Conversely, in order to allow an appropriate flow of the refrigerant through the supply pipe (124) and the collection pipe (125) during a clog elimination operation, a switching valve (128) is provided along the first high pressure pipe (108) and a switching valve (130) is provided along the suction side pipe (109). Note that an adsorber (131), and a switching valve (132) for preventing the backflow of water from the adsorber (131) during a cooling operation, may be provided along the collection pipe (125). Moreover, a flow rate control valve (133) may be provided along the collection pipe (125).
During a cooling operation, the switching valve (128) and the switching valve (130) are opened, while the switching valve (127) and the switching valve (129) are closed, whereby the high pressure helium gas discharged from the compressors (103, 104) is cooled through the first heat exchanger (121)xe2x86x92the first pre-cooling section (119)xe2x86x92the second heat exchanger (122)xe2x86x92the second pre-cooling section (120)xe2x86x92the third heat exchanger (123). Then, the high pressure helium gas expands through the JT valve (116) to be a liquid helium on a cryogenic level, and the liquid helium flows into a helium tank (136). A helium gas, which is generated through evaporation in the helium tank (136), flows into the suction side pipe (109) of the compressors (103, 104) through the low pressure line (118), and is compressed through the compressors (103, 104). Then, the circulation as described above is repeated.
During a clog elimination operation, the switching valve (128) and the switching valve (130) are closed, while the switching valve (127) and the switching valve (129) are opened, whereby the high pressure helium gas discharged from the compressors (103, 104) is supplied to the outlet side of the high pressure side passageway of the first heat exchanger (121) through the supply pipe (124), and flows backwards along the high pressure side passageway. Even if water is frozen in the first heat exchanger (121), the frozen ice is melted by the high pressure helium gas because a high pressure helium gas has a relatively high temperature. Then, the high pressure helium gas flows along the collection pipe (125) together with an impurity in the first heat exchanger (121), and flows into the suction side pipe (109) of the compressors (103, 104). As described above, a clog of the first heat exchanger (121) is eliminated, and an impurity is removed.
However, with the cryogenic refrigeration system (100), it is not possible to eliminate a clog occurring in a downstream side portion of the high pressure side passageway of the first heat exchanger (121), e.g., the second heat exchanger (122) or the third heat exchanger (123).
Moreover, the operation of the JT refrigerator (111) needs to be shut down temporarily during a clog elimination operation. Then, the liquid helium in the helium tank (136) is likely to evaporate, whereby the pressure inside the helium tank (136) increases. The conventional cryogenic refrigeration system (100) addresses the problem as follows. When the pressure inside the helium tank (136) increases excessively, a release valve (not shown) provided in the helium tank (136) is opened so as to release the helium gas into the atmosphere, thereby reducing the pressure. In this way, however, it is necessary to re-supply a significant amount of helium to the system after the completion of a clog elimination operation before a cooling operation can be resumed. This inevitably increases the running cost of the system.
The present invention has been made in view of these problems in the art, and has an object to provide a novel technique for a cryogenic refrigeration system, with which a clog can be eliminated over a wider area and which can contribute to a reduction in the running cost of the system.
A first cryogenic refrigeration system of the present invention includes: a compressor; a JT refrigerator including a JT valve through which a high pressure refrigerant gas discharged from the compressor is subjected to a Joule-Thomson expansion, and a refrigerant tank for storing the refrigerant, which has been liquefied by the Joule-Thomson expansion; a first heat exchanger, including a high pressure side passageway through which the high pressure refrigerant gas discharged from the compressor is passed and a low pressure side passageway through which a low pressure refrigerant gas from the refrigerant tank is passed, for exchanging heat between the high pressure refrigerant gas in the high pressure side passageway and the low pressure refrigerant gas in the low pressure side passageway; a pre-cooling refrigerator for pre-cooling the high pressure refrigerant gas, which has been cooled through the first heat exchanger, before the expansion through the JT valve; a first switching valve provided on an outlet side of the low pressure side passageway of the first heat exchanger; and a gas refrigerant collecting pipe including a second switching valve therealong and connecting the refrigerant tank with a pipe on a suction side of the compressor, wherein a clog elimination operation is performed, during which the JT valve is opened while the first switching valve is closed and the second switching valve is opened so that the refrigerant discharged from the compressor is passed at least through the high pressure side passageway of the first heat exchanger and the JT valve into the refrigerant tank while the refrigerant gas in the refrigerant tank is collected through the gas refrigerant collecting pipe.
A second cryogenic refrigeration system is similar to the first cryogenic refrigeration system, further including one or more heat exchanger, provided on a downstream side of the high pressure side passageway of the first heat exchanger, for exchanging heat between the high pressure refrigerant gas and the low pressure refrigerant gas.
A third cryogenic refrigeration system is similar to the first cryogenic refrigeration system, further including: a second heat exchanger and a third heat exchanger, provided on a downstream side of the high pressure side passageway of the first heat exchanger, for exchanging heat between the high pressure refrigerant gas and the low pressure refrigerant gas; a bypass pipe having one end thereof connected between the high pressure side passageway of the first heat exchanger and a high pressure side passageway of the second heat exchanger and the other end thereof connected between a high pressure side passageway of the third heat exchanger and the JT valve; and a switching valve provided along the bypass pipe, wherein during the clog elimination operation, the switching valve of the bypass pipe is opened so that the refrigerant discharged from the compressor is passed through the high pressure side passageway of the first heat exchanger, the bypass pipe and the JT valve into the refrigerant tank.
A fourth cryogenic refrigeration system is similar to the first cryogenic refrigeration system, further including: a second heat exchanger and a third heat exchanger, provided on a downstream side of the high pressure side passageway of the first heat exchanger, for exchanging heat between the high pressure refrigerant gas and the low pressure refrigerant gas; a bypass pipe having one end thereof connected between a high pressure side passageway of the second heat exchanger and a high pressure side passageway of the third heat exchanger and the other end thereof connected between,the high pressure side passageway of the third heat exchanger and the JT valve; and a switching valve provided along the bypass pipe, wherein during the clog elimination operation, the switching valve of the bypass pipe is opened so that the refrigerant discharged from the compressor is passed through the high pressure side passageway of the first heat exchanger, the high pressure side passageway of the second heat exchanger, the bypass pipe and the JT valve into the refrigerant tank.
A fifth cryogenic refrigeration system is similar to the first cryogenic refrigeration system, wherein an adsorber is provided along the gas refrigerant collecting pipe.
A sixth cryogenic refrigeration system is similar to the fifth cryogenic refrigeration system, further including a third switching valve provided between the adsorber of the gas refrigerant collecting pipe and the refrigerant tank, wherein the third switching valve is opened during the clog elimination operation and closed otherwise.
A seventh cryogenic refrigeration system is similar to the first cryogenic refrigeration system, wherein an adsorber is provided on an upstream side of the JT valve.
An eighth cryogenic refrigeration system includes: a compressor; a JT refrigerator including a JT valve through which a high pressure refrigerant gas discharged from the compressor is subjected to a Joule-Thomson expansion, and a refrigerant tank for storing the refrigerant, which has been liquefied by the Joule-Thomson expansion; a first heat exchanger, including a high pressure side passageway through which the high pressure refrigerant gas discharged from the compressor is passed and a low pressure side passageway through which a low pressure refrigerant gas from the refrigerant tank is passed, for exchanging heat between the high pressure refrigerant gas in the high pressure side passageway and the low pressure refrigerant gas in the low pressure side passageway; a pre-cooling refrigerator for pre-cooling the high pressure refrigerant gas, which has been cooled through the first heat exchanger, before the expansion through the JT valve; a first switching valve provided on an outlet side of the low pressure side passageway of the first heat exchanger; a gas refrigerant collecting pipe including a second switching valve therealong and connecting the refrigerant tank with a pipe on a suction side of the compressor; a second heat exchanger and a third heat exchanger, provided on a downstream side of the high pressure side passageway of the first heat exchanger, for exchanging heat between the high pressure refrigerant gas and the low pressure refrigerant gas; and a bypass pipe including a switching valve therealong and having one end thereof connected between the high pressure side passageway of the first heat exchanger and a high pressure side passageway of the second heat exchanger and the other end thereof connected between the JT valve and the refrigerant tank, wherein a clog elimination operation is performed, during which the JT valve is opened while the first switching valve is closed and the second switching valve and the switching valve of the bypass pipe are opened so that the refrigerant discharged from the compressor is passed through the high pressure side passageway of the first heat exchanger into the refrigerant tank while the refrigerant gas in the refrigerant tank is collected through the gas refrigerant collecting pipe.
A ninth cryogenic refrigeration system is similar to the eighth cryogenic refrigeration system, wherein an adsorber is provided along the gas refrigerant collecting pipe.
A tenth cryogenic refrigeration system is similar to the ninth cryogenic refrigeration system, further including a third switching valve provided between the adsorber of the gas refrigerant collecting pipe and the refrigerant tank, wherein the third switching valve is opened during the clog elimination operation and closed otherwise.
An eleventh cryogenic refrigeration system is similar to the eighth cryogenic refrigeration system, wherein an adsorber is provided on an upstream side of the JT valve.
A twelfth cryogenic refrigeration system includes: a compressor; a JT refrigerator including a JT valve through which a high pressure refrigerant gas discharged from the compressor is subjected to a Joule-Thomson expansion, and a refrigerant tank for storing the refrigerant, which has been liquefied by the Joule-Thomson expansion; a first heat exchanger, including a high pressure side passageway through which the high pressure refrigerant gas discharged from the compressor is passed and a low pressure side passageway through which a low pressure refrigerant gas from the refrigerant tank is passed, for exchanging heat between the high pressure refrigerant gas in the high pressure side passageway and the low pressure refrigerant gas in the low pressure side passageway; a pre-cooling refrigerator for pre-cooling the high pressure refrigerant gas, which has been cooled through the first heat exchanger, before the expansion through the JT valve; a first switching valve provided on an outlet side of the low pressure side passageway of the first heat exchanger; a gas refrigerant collecting pipe including a second switching valve therealong and connecting the refrigerant tank with a pipe on a suction side of the compressor; a second heat exchanger and a third heat exchanger, provided on a downstream side of the high pressure side passageway of the first heat exchanger, for exchanging heat between the high pressure refrigerant gas and the low pressure refrigerant gas; and a bypass pipe including a switching valve therealong and having one end thereof connected between a high pressure side passageway of the second heat exchanger and a high pressure side passageway of the third heat exchanger and the other end thereof connected between the JT valve and the refrigerant tank, wherein a clog elimination operation is performed, during which the JT valve is opened while the first switching valve is closed and the second switching valve and the switching valve of the bypass pipe are opened so that the refrigerant discharged from the compressor is passed through the high pressure side passageway of the first heat exchanger and the high pressure side passageway of the second heat exchanger into the refrigerant tank while the refrigerant gas in the refrigerant tank is collected through the gas refrigerant collecting pipe.
A thirteenth cryogenic refrigeration system is similar to the twelfth cryogenic refrigeration system, wherein an adsorber is provided along the gas refrigerant collecting pipe.
A fourteenth cryogenic refrigeration system is similar to the thirteenth cryogenic refrigeration system, further including a third switching valve provided between the adsorber of the gas refrigerant collecting pipe and the refrigerant tank, wherein the third switching valve is opened during the clog elimination operation and closed otherwise.
A fifteenth cryogenic refrigeration system is similar to the twelfth cryogenic refrigeration system, wherein an adsorber is provided on an upstream side of the JT valve.
With the first cryogenic refrigeration system, during the normal cooling operation, the high pressure refrigerant discharged from the compressor is cooled through the first heat exchanger, further cooled through the pre-cooling refrigerator, liquefied by the Joule-Thomson expansion through the JT valve, and then passed into the refrigerant tank. On the other hand, during the clog elimination operation, the high pressure refrigerant discharged from the compressor is passed through the high pressure side passageway of the first heat exchanger and the JT valve into the refrigerant tank. In this way, not only an impurity staying in the high pressure side passageway of the first heat exchanger, but also an impurity staying on the downstream side of the high pressure side passageway, is removed by the high pressure refrigerant. At least a portion of the gas refrigerant in the refrigerant tank is guided to the pipe on the suction side of the compressor through the gas refrigerant collecting pipe without being released into the atmosphere. Therefore, at least a portion of the gas refrigerant is not released into the atmosphere but is re-used for the cooling operation, thereby reducing the running cost of the system.
With the second cryogenic refrigeration system, a plurality of heat exchangers are provided and connected in series with one another, whereby not only a clog in the first heat exchanger, which is located at the most upstream position, but also a clog in another heat exchanger on the downstream side of the first heat exchanger, is eliminated.
With the third and eighth cryogenic refrigeration systems, it is possible to perform clog elimination exclusively for the first heat exchanger.
With the fourth and twelfth cryogenic refrigeration systems, it is possible to perform clog elimination exclusively for the first heat exchanger and the second heat exchanger.
With the fifth, ninth and thirteenth cryogenic refrigeration systems, the adsorber is provided along the gas refrigerant collecting pipe, whereby an impurity having flowed into the refrigerant tank is removed by the adsorber while the gas refrigerant in the refrigerant tank is collected through the gas refrigerant collecting pipe.
With the sixth, tenth and fourteenth cryogenic refrigeration systems, during the cooling operation, the third switching valve is closed, whereby the upstream side of the adsorber of the gas refrigerant collecting pipe is sealed, thus preventing the impurity having been adsorbed during the clog elimination operation from flowing back into the refrigerant tank during the cooling operation.
With the seventh, eleventh and fifteenth cryogenic refrigeration systems, the adsorber is provided on the upstream side of the JT valve, whereby an impurity staying on the downstream side of a high pressure side passageway of a heat exchanger is adsorbed and removed by the adsorber.
With the present invention, during the clog elimination operation, the high pressure refrigerant discharged from the compressor is supplied to the high pressure side passageway of the first heat exchanger and further to the downstream side of the high pressure side passageway, whereby not only a clog in the first heat exchanger, but also a clog in a passageway downstream of the first heat exchanger, can be eliminated. The gas refrigerant in the refrigerant tank is collected through the gas refrigerant collecting pipe during the clog elimination operation, whereby it is possible to suppress an increase in the pressure inside the refrigerant tank. Moreover, the collected refrigerant can be re-used for the cooling operation, whereby it is possible to reduce the running cost.